Electroacoustic transducer



2 Sheets-Sheet l June 27, 1967 F. MASSA ELECTROACOUSTIC TRANSDUCER FiledMarch 28, 1966 III llllll Ilnnillll INVENTOR.' WMA@ June 27, 1967 F.MASSA ELECTROACOUSTIC TRANSDUCER Filed March 28, 1966 @www XM. ATTORNEYSUnited States Patent O 3,328,751 ELECTRACOUSTIC TRANSDUCER Frank Massa,Cohasset, Mass., assignor to Massa Divi- 1ion, Dynamics Corporation ofAmerica, Hingham,

Filed Mar. 28, 1966, Ser. No. 537,899 24 Claims. (Cl. 340-10) Thisapplication is a continuation-impart of rny copending applicationentitled Electroacoustic Transducer, filed Feb. 15, 1962, Ser. No.173,510 now abandoned.

This invention relates generally to improvements in transducers fortransforming electrical energy to sound energy and more particularly tonew and improved electroacoustical transducers of the type adapted foroperating underwater within the audible frequency range.

Those skilled in the art appreciate that in the use of underwaterelectroacoustical transducers operating within the audio frequencyrange, it is necessary to drive relatively large radiating piston areasat appreciably large amplitudes of vibration if eflicient high powersound energy is to be generated. For the lower audio frequencies in therange of a few hundred to a few thousand cycles per second, it isadvantageous to build up the large radiating piston surface by a mosaicof several small modules arranged in a suitable array.

Accordingly, it is a primary object of this invention to provide uniquetransducer module constructions adapted for use in multiple arrays.

It is a further object of this invention to improve the efliciency of anelectroacoustic transducer adapted for radiating underwater sound withinthe audible frequency range.

It is another object lof this invention to reduce the overall size of anelectroacoustic transducer module by a unique construction which servesto distribute the internal weight of the operating elements in a moreadvantageous manner.

It is a still further object of this invention to reduce the cost of amanufacture of an efllcient underwater electroacoustic transducer.

It is still another object of this invention to improve the corrosionresistance of an electroacoustic transducer as well as to reduce theeffects of erosion due to cavitation which generally may occur at thevibrating surface of a high power transducer operating in shallow water.

It is still another object of this invention to provide a new andimproved flexible shock mounts for the transducer assemblies which areformed as integral parts of a transducer diaphragm protective structure.

A still further object of the invention is to provide transducerassemblies having imp-roved shapes to facilitate mounting in a multiplearray.

Yet another object of the invention is to provide transducer assembliesusing piezoelectric elements requiring high voltages, wherein voltagebreakdowns are obviated.

Still another object of the invention is to provide transducerassemblies incorporating impedance transformation means as a partthereof without substantially reversing overall size.

A still further object of the invention is to provide transducerassemblies in which the effects of contraction and expansion of partsfrom temperature changes are obviated.

The above and other objects of the invention will become evident in thefollowing detailed description. The novel features which arecharacteristic of the invention are set forth with particularity in theappended claims.

3,328,751 Patented June 27, 1967 ICC The invention itself, however, bothas to its organization and method of operation, as well as advantagesthereof, will best be understood from the following description ofseveral embodiments thereof when read in connection with theaccompanying drawings, in which:

v FIGURE l is a perspective View of one illustrative embodiment of theinvention;

FIGURE 2 is a vertical sectional view taken through the illustrativetransducer embodiment of FIGURE l;

FIGURE 3 is a partial vertical sectional view of a modification of theinvention wherein the use of piezoelectric crystal plates has beensubstituted for the polarized ceramic cylinder used in FIGURES l and 2embodiment;

FIGURE 4 is a sectional View taken substantially as shown along the line4 4 of FIGURE 2;

FIGURE 5 is a partial sectional view taken substantially as shown alongthe line 5 5 of FIGURE 4;

FIGURE 6 is a side elevational view of another modified form oftransducer assembly according to the principles of the invention;

FIGURE 7 is a vertical sectional view on an enlarged scale takensubstantially along line 7-7 of FIGURE 6;

FIGURE 8 is a top plan View of the assembly of FIG- URE 6; and

FIGURE 9 is a bottom plan View of the assembly of FIGURE 6.

Turning now to the drawings, and more specifically to FIGURES 1 and 2thereof, there is shown a preferred illustrative transducer constructionembodying some of the basic principles of the invention. A rigid,vibratile piston plate 10 is preferably made of a material having a highstiffness-to-mass ratio. For example, magnesium and aluminum alloy aresome of the materials that may advantageously be used. In accordancewith a feature of this invention, it is even more advantageous to employa type of aluminum casting which has a sponge-like structure and whichhas a density of only a fraction of solid aluminum and yet retains avery high stiffness for the piston plate 10 which is necessary in orderthat it will vibrate without break-up of its surface at the frequency ofoperation.

A transducer element 12, which may be a ceramic cylinder of polarizedbarium titanate or lead zirconate titanate or any other suitablematerial which is well known in the art for converting electrical energyto vibrational energy, is bonded at one of its ends to the plate 10 bymeans of a suitable cement 14. The opposite end of the transducerelement 12 is similarly bonded to the flat surface of a weight member16. Advantageously, the transducer element 12 has (-1-) and electrodes,as shown, to which insulated electrical conductors 18 and 2t! aresoldered. The conductors 18 and 20 are positioned through insulatingbushings 22 in the housing cap structure 30 and the ends of theconductors are soldered to the leads from a cable 24, as shown.

The recessed portion of the housing cap structure 30, within which theelectrical connections are made, is filled with a hard, insulatingcompound 52, such as epoxy, which serves to securely anchor the cable24.

A tubular housing structure 26 is formed with an inwardly turned flangeportion 28, which serves as a seat for the housing cap structure 30, andis preferably cemented in place thereat with a waterproof, stron-gcement 32, such as epoxy. At the opposite end of the lhousing structure26, there is an outwardly turned flange portion 34, whose outer contouris preferably the same as the outer contour of the plate 10.Advantageously, a resilient gasket 36 is cemented between the flangeportion 34 and the mating surface of the piston plate 10. In accordancewith this invention, the thickness and stiffness of the gasket 36material is selected such that the resonant frequency of the mass of thehousing structure 26 and the compliance of the gasket 36 occurs in arange well below the frequency of operation of the transducer assembly.It will be appreciated by those skilled in the art that this selectionis made so that at the frequency of operation of the transducerassembly, the vibrating plate will be uncoupled from the housingstructure 26 and thus, the housing structure 26 effectively will remainstationary which, in turn, prevents any undesirable radiation of soundfrom the rear of the transducer assembly. This advantageous constructionresults in improved efiiciency because only useful sound energy isradiated from the front face of the vibrating piston plate 10.

The plane surface of the Weight member 16 t-o which the cylindricaltransducer element 12 is attached preferably may be recessed as shown.This allows most of the weight member 16 to surround the cylindricaltransducer element 12 and thereby serves to keep the overall length ofthe assembly at a minimum and thus reduce the size of the transducer. Afurther advantage gained from this unique construction resides inthefact that the assembly is much more rugged to withstand shock andvibration than would be the case if the weight member 16 were extendedbeyond the ceramic cylinder transducer element 12 and thereby cause agreater stress at the cement joints 14 during transverse applications ofmechanical shock.

In the illustrative embodiment of FIGURE 2, the weight member 16 isshown as a hollow cup-shaped piece which surrounds the ceramictransducer element 12. As an alternative embodiment, the ceramiccylinder transducer element 12 may be formed with a large diameter andthe shape of the weight member 16 correspondingly modified so that thegreater part of the latter is in the form of a solid cylinder which tswithin the hollow cylinder transducer element 12. In such amodification, an enlarged peripheral flange end is machined on one endof the solid cylindrical weight member to permit the attachment of theweight member to the end of the ceramic transducer element. It can beseen that in this case, most of the weight would be placed inside theceramic cylinder transducer element instead of being placed outside theperiphery of the cylinder, as shown in the embodiment of FIG- URE 2.

In accordance with another feature of this invention, the reliability ofthe transducer under high power operation may further be increased bythe use of a bolt 38 to clamp the piston plate 10 and weight member 16to the transducer element 12. Advantageously, a spring washer 40 isselected so that its compression by the nut 4Z applies a sufficientforce to the assembly to prestress the cylinder transducer element 12 toa value greater than the stresses that will be developed at the joints14 during vibration o-f the cylinder transducer element at the maximumpower rating of the transducer assembly.

In order to prevent corrosion of the transducer assembly in salt waterenvironments, the structure described hereinabove may be completelycovered with a waterproof material, such as the rubber seal shown inFIGURES 1 and 2. This outer seal may comprise a rubber cylinder 44bonded to the outer periphery of the housing structure 26. A moldedrubber cap 46 is cemented over the end of the rubber cylinder 44, asillustrated. The cap 46 also may be provided with a molded taperedportion 48 which seals to the cable 24 and completes the waterproofingof the back end of the transducer assembly. At the front end of theassembly, a cap 50 of rubber or other waterproof material, is bonded tothe front radiating face of the plate 10. Preferably, the same rubbermaterial may 'be used to cover the outer sides of plate 10, continuingover the flange portion 34 and extending over part of the rubbercylindrical cover 44 thereby totally enclosing and sealing every exposedportion of metal in the assembly. As a result of this unique and highlyadvantageous arrangement, it is possible to employ low-cost, ordinarysteel for the housing structure, which reduces the cost of manufacture.

In order that the transducer performance be enhanced, it is desirablethat the weight member 16 be made greater than the weight of the soundgenerating piston plate 10. As a result of this construction, thevibration of the cylinder transducer element 12 will move the lighterpiston plate 16 to a larger degree than would be the case if the weightmember 16 were small compared to the weight of the piston plate 10. Thefront rubber cap 50 may be separately molded and then cemented in place,as shown in FIGURE 2, or it may be molded in place. It has been foundadvantageous to mold the rubber cap 50 in place and, at the same time,to incorporate molded shock mounts in the corners of the front face forisolating the transducer assembly from its mounting, as will be morefully described hereinbelow with respect to the embodiments of FIGURES1, 4 and 5.

FIGURE 3 illustrates an alternative embodiment which utilizespiezoelectric crystal plates 54 as the transducer material in place ofthe ceramic cylinder 12 shown in FIG- URE 2. The crystal plates 54 maybe 45 Z-cut ammonium diphydrogen phosphate or any other piezoelectriccrystal well known in the art and capable of converting electricalsignals to mechanical vibrations. In accordance with a feature of thisinvention, the crystal plates have (1+) and electrode bearing faceswhich are connected with like polarities together, as shownschematically in FIGURE 3, and the like polarities are connected to theelectrical conductors 18 and 20 which serve the same function as theleads shown in FIGURE 2 and identified by the same reference numerals.

FIGURE 4 is a sectional View taken along the line 4-4 of FIGURE 2, andillustrates one preferred embodiment of shock mounts 58 which are formedas part of the rubber molding associated with the transducer face. FIG-URE 5 is a partial sectional view taken along the line 5 5 of FIGURE 4.It can be seen that the dotted line in FIGURE 4 defines the contour ofthe vibratile piston plate 10 in which the corners are chamfered toallow the space for molding a rubber shock mount 58 in each corner ofthe transducer assembly. The view in FIGURE 5 shows the general shape ofthe molded rubber cap 50, which provides a complete watertight coveringfor the radiating face and the side edges of the piston plate 10. Thisarrangement results in the provision of four rubber mounts 58 having theclearance holes 56. Those skilled in the art will appreciate that thispermits the transducer assembly to be resiliently mounted at its fourcorners when it is installed into its mounting support for operation.

Referring now to FIGURES 6-9, reference numeral 60 generally designatesa transducer assembly having a modied construction. The assembly 60comprises a rigid vibratile piston plate 61 which is similar to thepiston plate 10 and is preferably made of a material having a highstiffness-to-mass ratio. For example, magnesium and aluminum alloys aresome of the materials that may advantageously be used. In accordancewith a feature of this invention, it is even more advantageous to employa type of aluminum casting which has a sponge-like structure and whichhas a density of only a fraction of solid aluminum and it retains a veryhigh stiffness for the piston plate 61 which is necessary in order thatit will vibrate without break-up of its surface at the frequency ofoperation.

A transducer unit generally designated by reference numeral 62 isprovided which comprises four cylindrical elements 63-66 in end-to-endrelation and having electrode means on the end faces thereof.Preferably, the elements 63-66 may be ceramic cylinders of polarizedbarium titanate or lead zirconate or any other suitable material whichis well known in the art for converting electrical energy to vibrationalenergy. Advantageously,

the elements 63-66 are polarized as indicated by the and indications onthe drawing, with faces of like polarity in abutting relation. To supplyelectrical energy to the transducer elements, the electrode on one faceof the element 63 is extended to provide a lead 67; one of theelectrodes on the abutting faces of the elements 63 and 64 is extendedto provide a lead 68; one of the electrodes on the abutting faces ofelements 64 and 65 is extended to provide a lead 69; one of theelectrodes on the abutting faces of elements 65 and 66 is extended toprovide a lead 70; and the electrode on the other face of element 66 isextended to provide a lead 71. Lead 71 is connected through a conductor72 to the lead 69 which is connected through a conductor 73 to the lead67, lead 67 being connected to a conductor 74. Lead 70 is connectedthrough a conductor 75 to the lead 68 Which is connected to a lead 76.By application of a high Voltage to the conductors 74 and 76, thetransducer unit 62 may be operated at a high power output level.

A weight member 78 is secured against the end face of the element 63which carries the electrode 67, preferably with a thin insulating washer79 being provided. At the opposite end of the transducer unit 62, theend face of the element 66 is disposed against a central portion of thevibratile element 61, preferably with a thin insulating washer 81 beingprovided.

To hold the weight member 78, transducer unit 62 and vibratile plate 61in assembly, securing means are provided Which comprise a bolt 83 havinga head portion 84 and a shank portion 85 extending through an opening 86in the weight member 78 with an end portion 87 of the shank portion 85being threaded into an opening 88 in the vibratile plate 61. Inaccordance with a specific feature of the invention, a plurality ofBelleville springs 90 are disposed between a collar 91 engaged by thehead 84 and a weight surface of a recess 92 in the base member 78. Thesprings 90 are cup-shaped washers which behave as springs of relativelyhigh stiffness and when the bolt 83 is tightened, the basic vibratingelements of the assembly are held together with substantially uniformpressures between the end faces of the transducer unit 62 and the weightmember 78 and vibratile plate 61. Without the compression springs, thetension in the bolt 83 would be a function of temperature because ofdifferences in thermal expansion of the various materials which make upthe complete vibrating structure. With the spring elements 90 compressedby a fractional part of an inch, variations in dimensions of ltheassembled parts of a few thousands of an inch will be negligible indetermining the applied compressive force to the assembled elements.

A hollow rigid housing structure 94 is provided in surrounding relationto the transducer unit 62 and the weight member 78 with resilient meansin the form of an annular gasket 96 being disposed between an open endof the housing structure 94 and a peripheral portion of the vibratileplate 61. As shown, the gasket 96 is disposed between facing surfaces 97and 98 of the plate 61 and the housing 94, respectively, the surfacesn97 and 98 being planar surfaces transverse to the axis of vibratilemovement of the plate 61. Preferably, the gasket 96 is cemented to thesurfaces 97 and 98 with strong waterproof cement such as an epoxy. Itwill be noted that the gasket 96 compresses and expands with vibratilemovement of the plate 61 and when the assembly is placed under water,the water pressure compresses the gasket 96 to a certain degree, toinsure an effective seal.

In accordance with the invention, the thickness and stiffness of thegasket 96 is selected such that the resonant frequency, determined bythe mass of the housing structure 94 and the compliance of the gasket 96occurs in a range well below the frequency of operation of thetransducer assembly. With this arrangement, the vibrating plate 61 Willbe uncoupled from the housing structure 94 and thus the housingstructure 94 can effectively remain stationary to prevent anyundesirable radiation of sound from the rear of the transducer assembly.This advantageous construction results in improved efficiency becauseonly useful sound energy is radiated from the front face of thevibrating piston plate 61.

According to a specic 4feature of the invention, the hollow rigidhousing structure 94 is tapered, the diameter or transverse dimensionthereof at the open end which is adjacent the plate 61 beingsubstantially greater than the diameter or transverse dimension at theopposite end thereof. This arrangement permits the assembly of a numberof transducer assemblies within a minimum circle diameter so that amaximum power density can be achieved with an overall structure which isquite compact.

Preferably, the weight member 78 has an outer surface 99 which has ataper corresponding to that of the wall of the housing structure 94, soas to permit the weight member 78 to have a maximum size relative to theoverall size of the assembly.

A further feature of the invention is in the provision of a couplingtransformer 100' which is supported on the outside of an end wall 101 ofthe housing structure 94 preferably by means of a molded pottingcompound 102 which encloses the transformer 100. The transformer 100 isof conventional construction, including a three-legged core structure103 formed of stacked laminations with primary and secondary windings104 on a center leg of the core 103, the secondary Winding beingconnected to l the conductors 74 and 76 and the primary winding beingconnected through conductors 105 and 106 to conductors of a waterproofcable 108, the end of the cable 108 being enclosed in the pottingcompound 102.

To prevent corrosion of the assembly in salt water environments, a coverof waterproof material is bonded to a radiating face 110 of thevibratile plate 61 and completely encloses the housing structure 94 toprovide a water-tight seal Iaround the transducer assembly. Inparticular, a molded rubber cap 111 is provided having an internalcontour of the same shape as the contour of the radiating face 110, theinternal surface of the cap 111 being bonded to the face 110 -by meansof a suitable cement, such as an epoxy. Preferably the cap 111 may bemolded directly to the surface of the piston 110 by curing the Irub-bercompound in a mold using the piston 110 as an insert. The cap 111 has anintegral annular flange portion 112 which embraces a peripheral edge 113of the plate 61 and which embraces an end portion of the housingstructure 94.

In accordance with a specific feature of the invention, the cap 111 isgenerally rectangular, preferably substantially square as shown inFIGURES l8 and 9, and the four corner portions thereof are so formed asto be thinner than the plate 61 and as to define integral mounting tabportions 114, the portions 114 being preferably provided with openings115 therethrough, for mounting on a rigid support structure.

The rubber cover 4further comprises a tapered or frustoconical rubbersleeve 116 which surrounds the housing structure 94 and preferably alsosurrounds the molded potting compound 102 which surrounds thetransformer 110. An end portion 117 is preferably disposed within theflange portion 112 of the cap 111, and the outer surface of the housingstructure 94 is recessed for this purpose.

In accordance with a further specific feature, the rubber sleeve member116 is provided with a plurality of peripherally spaced tapered integralWedge portions which serve as additional shock mounts when thetransducer is l assembled into a frame-like mounting structure. Thus,

the mounting structure may include a portion having an internalcylindrical surface for engagement by the tapered Wedge portions 118.

The rubber cover Afor the assembly further includes a cap 120 having anannular flange portion 121 surrounding an end portion of the sleeve 116.The cap 120 addi- 7 tionally has a strain relief extension 122 whichembraces the cable 108.

Still another feature of the invention relates to the prevention ofvoltage breakdowns within the transducer assembly while permittingapplication of high voltages to the transducer elements 63-66, to obtainhigh power operation thereof. In accordance with this feature, openings123 and 124 are provided in the end wall 101 of the housing structure94, to permit the space within the housing structure 94 and around thetransducer unit 62 to be filled with an inert dry gas, after the plate61 is secured to the open end of the housing structure 94 through thewasher 96. After filling the space with an inert dry gas, rubber plugs125 and 126 are inserted in the openings 123 and 124, after which thetransformer 110 and potting compounds 102 are installed. Thereafter, thecap 111, sleeve 116 and cap 120 are installed to provide the waterproofcover.

It will be understood that modifications and variations may be effectedwithout departing from the spirit and scope of the novel concepts ofthis invention.

I claim as my invention:

1. In an electroacoustic transducer assembly, transducer means havingopposite end surfaces, a weight member secured against one of said endsurfaces of said transducer means, a vibratile plate having a radiatingface on one side thereof and having a central portion on the oppositeside thereof secured against the other of said end surfaces of saidtransducer means, a hollow rigid housing structure surrounding saidtransducer means and said weight member and having an open end ladjacenta peripheral portion of said vibratile plate, and resilient meansinterposed between said open end of said housing structure and saidperipheral portion of said vibratile plate arranged to flexibly sealsaid housing structure to said vibratile plate.

2. In an electroacoustic transducer assembly as defined in claim 1, saidresilient means being arranged to compress and expand with vibratilemovement of said plate relative to said housing structure.

3. In an electroacoustic transducer assembly as defined in claim 2, saidhousing structure and said vibratile plate having facing surfaces inparallel planes generally transverse to the direction of vibratilemovement of said plate relative to said housing structure, and saidresilient means being of washer-shaped configuration interposed betweensaid facing surfaces.

4. In an electroacoustic transducer assembly as defined in claim 1, thecompliance of said resilient means and the mass of said rigid housingbeing such as to resonate at a frequency lower than the frequency ofoperation of said transducer assembly.

5. In an electroacoustic transducer assembly as defined in claim 1, acover of Waterproof material bonded to said radiating face of saidvibratile plate and completely enclosing said housing structure toprovide a water-tight seal around said transducer assembly.

6. In an electroacoustic transducer assembly as defined in claim 1, amolded cup-shaped member of resilient waterproof material receiving saidvibratile plate therewithin and extending around said resilient meansand around said open end of said housing structure.

7. In an electroacoustic transducer assembly as defined in claim 1, acover member of resilient material bonded to said radiating face of saidvibratile plate and having integral mounting tab portions projectingfrom the periphery thereof.

8. In an electroacoustic transducer assembly as defined in claim 1, saidtransducer means being shaped as a hollow cylinder having parallelplanar end faces transverse to the axis thereof to define said oppositeend surfaces.

9. In an electroacoustic transducer assembly as defined in claim 8, saidtransducer means comprising a plurality of cylindrical elements onedisposed concentrically within another With the outer cylindricalsurface of one element against the inner cylindrical surface of anotherelement, and electrode means on the cylindrical surfaces of saidelements.

10. In an electroacoustic transducer assembly as defined in claim 8,said transducer means comprising a plurality of cylindrical elements inend-to-end relation and having planar end faces in abutting relation,and electrode means on the end faces of said elements.

11. In an electroacoustic transducer assembly as defined in claim 8,securing means extending from said weight member through said transducermeans to said vibratile plate to hold said weight member and saidVibratile plate tightly against said end faces of said transducer means.

12. In an electroacoustic transducer assembly as defined in claim 11,said securing means comprising compressible spring means, a bolt memberextending through said compressible spring means, and means on said boltmember for compressing said spring means to develop a spring forceholding said vibratile plate and said weight member against said endfaces of said transducer means with a substantially uniform pressure.

13. In an electroacoustic transducer assembly as defined in claim 12,said compressible spring means comprising at least one cup-shaped washeroperative as a spring having relatively high stiffness.

14. In an electroacoustic transducer assembly as defined in claim 1,said transducer means including a piezoelectric crystal plate formed of45 degree Z-cut ammonium diphydrogen phosphate.

15. In an electroacoustic transducer assembly as defined in claim 1,said hollow rigid housing structure being tapered from a largetransverse dimension at said open end to a small transverse dimension atan opposite end position beyond said weight member.

16. In an electroacoustic transducer assembly as defined in claim 15, acover of resilient material against the outer surface of said hollowrigid housing structure, and a plurality of peripherally spaced integraltapered wedges on said cover for defining shock mounts for mounting ofsaid transducer assembly in a frame-like mounting structure.

17. In an electroacoustic transducer assembly as defined in claim 1, atransformer having a primary and secondary winding, potting materialenclosing said transformer and supporting said transformer on saidhousing structure beyond said weight member, conductor means connectingone of said windings to said transducer means, and cable means connectedto the other of said windings.

18. In an electroacoustic transducer assembly as defined in claim 17,said housing structure having an end wall beyond said weight member withsaid potting material and said transformer being positioned on the outerside of said end Wall, and a cover of waterproof material bonded to theradiating face of said vibratile plate and completely enclosing saidhousing structure and said pottting material to provide a water-tightseal around said transducer assembly.

19. In an electroacoustic transducer assembly as defined in claim 18,said cable being waterproof, and said cover including an integralstrain-relief extension sealingly fitted over said cable.

20. In an electroacoustic transducer assembly as dened in claim 1, saidweight member having a portion projecting toward said vibratile Iplatein spaced relation to said transducer means such that a substantialportion of the mass of said Weight member lies within a region definedby spaced apart parallel planes intersecting said opposite end surfacesof said transducer means.

21. In an electroacoustic transducer assembly as defined in claim 20,said projecting portion of said weight member being in the form of anannular flange portion surrounding said transducer means.

22. In an electroacoustic transducer assembly as defined in claim 1,said transducer means including piezoelectric elements having electrodesthereon, conductor means for applying high voltages to said electrodesfor high power operation of said transducer means, and an inert dry gaslling the space within said housing structure surrounding saidtransducer means.

23. In an electroacoustic transducer assembly as defined in claim 1,said weight member shaped as a truncated cone with the large diameter ofsaid weight member placed in Contact with said transducer means.

24. In an electroacoustic transducer assembly as defined in claim 23,said hollow rigid housing structure being tapered from a largetransverse dimension at said open end to a small transverse dimension aton opposite end position beyond said truncated cone shaped weight memberwherein the large diameter of said weight member is placed in contactwith said transducer means.

References Cited UNITED STATES PATENTS Sawyer et a1. 340-10 Batchelder.

Miller 340-10 Grisdale et al.

Crandell 340-10 Mattei et al.

Harris 340-10 Massa 340-10 Ehrlich et al 340-10 Elliot et al. 340-10RODNEY D. BENNETT, Primary Examiner. I. P. MORRIS, Assistant Examiner.

Disclaimer 3,328,751.-Frcmk Massa, Cohasset, Mass. ELECTROACOUSTICTRANS- DUCER. Patent dated June 27, 1967. Disclaimer filed Apr. 10,1980, by the Stonelez'gh Trust of C'ohasset, M ass., represented byDonald P. Massa. and Fred M. Dellorfano, Jr. (Co-Trustees).

Hereby enters this disclaimer to claims 10, 15, 16, 17, 18, 19, 22, 23and 24 of said patent.

[Official Gazette, June 17, 1.980.]

1. IN AN ELECTROACOUSTIC TRANSDUCER ASSEMBLY, TRANSDUCER MEANS HAVINGOPPOSITE END SURFACES, A WEIGHT MEMBER SECURED AGAINST ONE OF SAID ENDSURFACES OF SAID TRANSDUCER MEANS, A VIBRATILE PLATE HAVING A RADIATINGFACE ON ONE SIDE THEREOF AND HAVING A CENTRAL PORTION ON THE OPPOSITESIDE THEREOF SECURED GAINST THE OTHER OF SAID END SURFACES OF SAIDTRANSDUCER MEANS, A HOLLOW RIGID HOUSING STRUCTURE SURROUNDING SAIDTRANSDUCER MEANS AND SAID WEIGHT MEMBER AND HAVING AN OPEN END ADJACENTA PERIPHERAL PORTION OF SAID VIBRATILE PLATE, AND RESILIENT MEANSINTERPOSED BETWEEN SAID OPEN END OF SAID HOUSING STRUCTURE AND SAIDPERIPHERAL PORTION OF SAID VIBRATILE PLATE ARRANGED TO FLEXIBLY SEALSAID HOUSING STRUCTURE TO SAID VIBRATILE PLATE.